The present invention relates to S-adenosylmethionine-6-N-lysine-methyltransferase (LMT) obtained from Neurospora crassa, a polynucleotide encoding the same, a vector and host cell containing the polynucleotide, and a method of producing trimethyllysine by culturing the host cell.
L-carnitine (3-hydroxy-4-trimethylaminobutyrate) generally exists in organisms and is a zwitterionic compound that carries long-chain activated fatty acids into the mitochondrial matrix across the inner mitochondrial membranes in the mitochondria. It is known that L-carnitine in the human body can be synthesized from lysine or protein lysine. Generally, in a mammal, protein lysine is used as a precursor of L-carnitine biosynthesis, but free lysine is used in Neurospora crassa. In L-carnitine biosynthesis, ε-N,N,N-trimethyllysine, ε-N,N,N-trimethyl-β-hydroxyllysine, a N,N,N-trimethylamino butyraldehyde intermediate, and γ-butyrobetaine are produced, and it is supposed that γ-butyrobetaine is hydroxylated by γ-butyrobetaine hydroxylase to become L-carnitine.
Even in the prior art, when L-carnitine is biosynthesized from free lysine in Neurospora crassa, an enzyme participating in the first step reaction of converting ε-N,N,N-trimethyllysine to L-lysine is not known. The enzyme can be usefully employed in producing L-carnitine from free lysine.
The inventors of the present invention have tried to produce a microorganism that uses an inexpensive precursor and also has a high production efficiency of L-carnitine, and found a protein and gene having activity of converting L-lysine from Neurospora crassa to 6-N-trimethyllysine, thus completing the present invention.